The invention relates to a hydraulic traction mechanism tensioning unit for a traction mechanism drive of a motor vehicle.
It is generally known that traction mechanism tensioning units are mainly used for compensating for production tolerances, traction mechanism elongation, and wear. Here, a tensioning effect is realized by the traction mechanism tensioning unit that acts, via a tensioning rail, on the traction mechanism, usually a chain or a belt.
From DE 10 2012 223 329 A1, a hydraulic traction mechanism tensioning unit is disclosed. This unit comprises a tensioner housing with a cylinder, a piston that is guided so it can move longitudinally and defines, with the cylinder, a hydraulic compression chamber, a hydraulic supply space defined by the tensioner housing and by the cylinder and a non-return valve that connects the supply space to the compression chamber. The non-return valve closes when the pressure in the compression chamber exceeds the pressure in the supply space. The traction mechanism tensioning unit also comprises a pressure relief valve that connects the compression chamber to the supply space, wherein the pressure relief valve opens when the pressure in the compression chamber exceeds a specified limit pressure. In addition, the traction mechanism tensioning unit comprises a control valve that can be switched between an open and a closed position and, in the open position, permits flow via the pressure relief valve and, in the closed position, prevents flow via the pressure relief valve.